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Preliminary Results of Effect of Sizings on Enzyme

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Preliminary Results of Effect of Sizings on Enzyme In: Proceedings of the 1994 TAPPI Recycling symposium; 1994 May 15-18; Boston, MA. Atlanta, GA: TAPPI Press: 1994: 103-105. PRELIMINARY RESULTS OF EFFECT OF Enzymes are proteins that react with specific substrates upon SIZINGS ON ENZYME-ENHANCED DEINKING attachment. Attachment occurs through random diffusion and specific molecular interaction. Enzymes carry ionic charges Kathie Rutledge-Cropsey John H. Klungness and have hydrophobic and hydrophilic characteristics that Technologist Chemical Engineer assist in their attachment to substrates. Binding domains align Thomas Jeffries Marguerite Sykes the catalytic site with the band to be acted upon and facilitate Microbiologist Technologist the degradation of polymers. Likewise, fibers carry ionic USDA Forest Service USDA Forest Service charges and can be hydrophilic or hydrophobic, depending on Forest Products Laboratory1 Forest Products Laboratory their degree of exposure to papermaking additives. Specifi- Madison, Wisconsin U.S.A. Madison, Wisconsin U.S.A. cally, sizing agents such as alkenyl succinic anhydride (ASA). alkyl succinic anhydride (AKD), and rosin/alum make fibers hydrophobic (8). ABSTRACT The first requirement for enzyme action is that its catalytic site must be able to make contact with the substrate in a productive This report presents results of preliminary research on whether complex. Formation of such a complex can be prevented (a) if enzymatic deinking is affected by the physical presence of the fiber is not readily wettable, and hence enzyme diffusion acid and alkaline sizings or by the hydrophobic nature of sized to the fiber surface cannot occur, (b) if the substrate is fibers. Three commercial xerographic papers printed with chemically modified in such a way that the binding domain styrene acrylate toner were sized with different agents (rosin/ does not attach, or (c) if covalent modification of the substrate alum, alkenyl succinic anhydride, and alkyl succinic sterically hinders the catalytic domain. Therefore, it may be anyhydride) and tested for water resistance. Deinking included possible for fiber characteristics to influence enzyme attach- medium consistency pulping with enzymes followed by ment or catalytic activity and, ultimately, deinking efficiency. flotation and dewatering. The results were based on image analysis of handsheets and Cobb testing. Papers sized with This study is an extension of previous work in our laboratory alkenyl succinic anhydride were the easiest to deink; the most on enzymatic &inking of acid and alkaline nonimpact printed hydrophobic paper (paper sized with rosin/alum) was the most paper (5,6). In the present study, we examined the effect of difficult to deink. Deinking efficiency was also affected by the internal sizing on the efficacy of enzyme-enhanced deinking. water resistance of the sheet prior to repulping, as measured by the Cobb test. Paper with high water resistance had poor RESULTS AND DISCUSSION deinking efficiency. Our earlier studies (5.6) established optimum cellulase dosage levels, reaction time, and temperature. Based on these results, KEYWORDS we used only one level of enzyme, reaction time, and tempera- ture in the present study. Image analysis results are illustrated in Figure 1. All samples INTRODUCTION contained approximately 14,200 ppm of ink after initial fiberization. Enzyme pulping of the ASA-sized paper resulted Several studies have shown that enzymes such as cellulases, in the lowest level of residual ink (22 ppm). Residual ink of hemicellulases, and xylanases effectively deink wastepapers. the ASA water control was also lower than that of the other Researchers have studied enzymatic deinking on newsprint samples. As seen in Figure 2, the high Cobb values of 73 and (l-3) and nonimpact printed papers (1,4-6). These studies 72 g/m2 wire and felt sides, respectively, for the ASA paper have explored enzymatic deinking under realistic pulping show that the paper was easily wetted. This may have contrib- conditions by using postconsumer or commercially available uted to the higher deinking efficiency of the water control. basestocks and have achieved good results. As stated by Zeyer However, it is not clear why the ASA control value was et al. (7), it is important to consider that paper sizings and significantly lower than that of the other controls. coatings can effect enzymatic deinking. Our investigation suggests that internal sizings may lower efficiency of Deinking efficiency was calculated from the difference in residual amount of ink between enzymatically deinked and enzymatic deinking. water control accepts divided by the amount of water control accepts. The rosin/alum paper had the lowest deinking efficiency as shown in Figure 3. The rosin/alum paper had 1The Forest Products Laboratory is maintained in cooperation Cobb values of 22 and 21 g/m2 for wire and felt sides, respec- with the University of Wisconsin. This article was written and tively. This paper had the highest water resistance of the three prepared by U.S. Government employees on official time, and it papers, which may be why it was the most difficult to deink is therefore in the public domain and not subject to copyright. (Fig. 2). 1994 Recycling Symposium / 103 The Cobb values for the AKD paper were 38 and 40 g/m2 for wire and felt sides, respectively, indicating high water resistance. Next to the rosin/alum paper, the AKD paper had the second lowest deinking efficiency (6.4% Fig. 1). The poor deinkability of the AKD paper may have been caused by the tendency of AKD to tenaciously maintain its covalent bond with cellulose during repulping. Researchers found that only a small amount of AKD could be extracted from cellulose using solvents (9). After dissolving AKD-treated fibers with cuprammonium, only a AKD shell remained (9). This could physically prohibit the enzyme from attacking the fiber during enzyme pulping. Figure 1: Residual ink after enzymatic deinking. As expected, when a 50/50 mixture of AKD- and ASA- sized papers was treated with enzymes and deinked, the result was a significant improvement in deinkability compared to that of the AKD sample (Fig. 3). CONCLUDING REMARKS The most effective enzymatic deinking on the standard styrene/acrylate printed papers in this study was accom- plished with ASA-sized paper, which had low water resistance. The AKD-sized and rosin/alum-sized papers had significantly higher water resistance and were also much more difficult to deink enzymatically. It is unclear whether deinkability is limited by the type of sizing agent present or by the hydrophobicity of the fibers. To clarify this problem, we intend to study the deinkability of papers sized with ASA, AKD, and rosin/alum at different levels of water Figure 2: Effect of water resistance on enzyme resistance. deinking efficiency. EXPERIMENTAL Paper Furnish Three commercial brands of xerographic papers were chosen for this experiment. Each brand had either rosin/ alum sizing, ASA, or AKD internal sizing. The papers were printed on a Sharp SF-88701 copier using a styrene acrylate toner. A standard test print with approximately 16% ink coverage was applied to each sheet. A weight of 250 g ovendry (O.D.) solids was shredded for each experiment. Pulping Each batch was soaked in reverse-osmosis purified water at 15% consistency overnight. Prior to testing, the pulp was warmed to 55°C in a water bath. Figure 3: Deinking efficiency. 1The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service. 104 / TAPPI Proceedings Enzyme Treatment The pulp was fiberized in a 5-L Hobart mixer at 12% consistency, 55°C for 15 min. The mixing bowl was jacketed to maintain a constant temperature. During this period, alkalinity was adjusted to approximately pH 7 with sulfuric acid. Next, a dilute solution of 0.2-ml Novo Nordisk SP-342 was slowly added to the pulp during mixing. The resulting consistency was 11% Total enzyme reaction time was 20 min. Water Control The same procedure was used with the water controls as with the enzyme samples except that water was substituted for the diluted enzyme. Flotation and Dewatering Immediately following pulping at 11% consistency, 80 g O.D. pulp was diluted to 1% consistency and transferred to an 8-L capacity laboratory Denver cell. After thorough mixing, DI-600 nonionic flotation aid (High Point Chemi- cals, High Point, North Carolina) was added at a rate of 0.1% on solids. The slurry was mixed for 1 min and floated for 3 min at 1,200 rpm. The flotation accepts were poured over a Tyler mesh 80 (0.177 mm) sidehill screen for dewatering. Handsheet Preparation and Testing Handsheets of the pulp samples and accepts were made with a British handsheet mold according to TAPPI T-205. Particle count was performed on a Hewlett Packard Scan Jet IIc and analyzed with software by Optomax, Burlington, Massachusetts. The particle range was 0.02-2.00 mm2. Four handsheets from each experiment were tested on both felt and wire sides. Cobb size testing was performed according to TAPPI T-441 for 60 s. LITERATURE CITED 1994 Recycling Symposium / 105.
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